ELECTROHYDRAULIC LIFTING DEVICE

Abstract: The present invention proposes a solution to the problem caused by the nonalignment, with respect to a horizontal plane, of the support platforms (1, 2) in an electrohydraulic lifting device equipped with two support platforms. The nonalignment occurs in the raising and lowering stages and the invention allows for controlling continuously the height of the support platforms (1, 2) and for promptly carrying out the necessary adjustment to set again the support platforms (1, 2) in alignment with each other.

Description: ELECTROHYDRAULIC LIFTING DEVICE TECHNICAL FIELD The invention relates to an electrohydraulic lifting device, in particular a heavy load lifting device including two support platforms, wherein raising and lowering of each support platform are controlled independently from the other platform and, when necessary, compensated, e.g. when a dif¬ ference occurs in the heights of the two support platforms. A compensation electrohydraulic system is controlled by an electronic control unit that oper- ates in real-time. BACKGROUND ART Electrohydraulic lifting devices are known, which include support platforms and are adapted to raise and lower a load that has been put onto the platforms. These lifting devices work in such a manner, so as to keep the load always in horizontal posi¬ tion, as far as possible. This kind of lifting devices basically in¬ clude: - two support platforms, which are parallel to each other and supported by related structures indepen¬ dent from each other. The structures are made in a way so as to define for the support platforms two extreme positions, namely a lowered position and a raised position,- - one, or more than one, hydraulic cylinders for each of the support platforms, the cylinders being independently fed through respective parallel con¬ duits (including cutoff solenoid valves) . The stems of the cylinders are synchronically moved as a consequence of a rigid mechanical link connected to the means actuated by the same stems,- - an electrohydraulic control unit connected to the cylinders of each pair via an oil flow splitting valve. The task of this last valve, during either the feeding or discharge, is to subdivide the oil volume displaced into smaller equal volumes which are delivered to two pipes each of which splits into two branches connected to the related cylinders of the respective platforms. The above mentioned lifting device has a problem in keeping the platforms in alignment with each other, with respect to a horizontal plane, and this problem has never been easy to solve. A difference can occur in the flow of hydrau¬ lic pressure media delivered to the above mentioned pairs of cylinders through the said conduits, when one of the two conduits presents a hydraulic flow resistance different from the other one. This difference in flow resistance is caused either by the load not being regularly distributed on the support platforms, or by small defects in designing and manufacturing the hydraulic circuits and the mechanical-electromechanical components of the lifting device. In this case the fluid tends to run through the one of the two conduits that has the lowest hydraulic flow resistance. Consequently, the two platforms locate at different height levels, and the load takes an inclined position in accordance with this differ- ence. The drawback that has just been described is rather dangerous for the people working in the area around the lifting device, and cannot anyway be accepted in view of a technical consideration. Configurations which have been designed and manufactured in the intention of solving, at least partially, the above mentioned problem, have so far included flow splitting valves more and more sophisticated, and thus expensive and needing an uneasy complex maintenance. These valves have only limited the problems without solving them. A further known device includes a transversal link between the two of the support platforms, this link including mechanical means, such as torsional bars. DISCLOSURE OF THE INVENTION The main object of the present invention is to find a solution to these problems, that is to the horizontal nonalignment of one platform in respect of the other one that occurs during the raising and lowering stages in an electrohydraulic lifting de- vice, without providing any mechanical transversal link between the two of the support platforms. In the way suggested by the invention the height level of each platform is checked second by second and any adjustment, necessary to set again the platforms in reciprocal alignment, is immediate¬ ly carried out. The above mentioned object is achieved by means of an electrohydraulic lifting device, includ¬ ing: at least two support platforms set substantially parallel to each other and carried by related struc- tures made in such a way as to define two extreme positions for the platforms, namely a lowered posi¬ tion and a raised position respectively; at least two hydraulic cylinders, namely a first cylinder and a second cylinder, each arranged for operating a respective one of the said structures,- a flow splitting valve connected at one side to pipes, namely a first pipe and a second pipe each connected to a related one of the said hydraulic cylinders,- an electro-hydraulic central unit connected, through a main conduit, to the other side of the said flow splitting valve and provided for feeding the said hydraulic cylinders,- a first duct aimed at connecting said first pipe with said main conduit, via a first synchronising solenoid valve,- a second duct aimed at connecting said second pipe with said main .conduit, via a second synchronising solenoid valve,- a first sensor means aimed at detecting the length of the part of the stem that is outside the related first hydraulic cylinder,- a second sensor means aimed at detecting the length of the part of the stem that is outside the related second hydraulic cylinder,- an electronic unit, to which the said first and second synchronising solenoid valves as well as the said first and second sensor means are connected, the said electronic unit being designed to process the electronic signals supplied to it by the said sensor means and to operate the one or the other of the said synchronising solenoid valves, as a conse¬ quence of a negative or positive value of the dif- ference between the parts of the said stems coming out from the respective cylinders, so that this difference is made to fall within a prefixed toler¬ ance range. BRIEF DESCRIPTION OF THE DRAWINGS The characteristic features of the invention are set out in the following, with particular refer¬ ence to the only one accompanying drawing, in which the lifting device, that is the subject of the present invention, is schematically shown. BEST MODE OF CARRYING OUT THE INVENTION With reference to the above mentioned draw¬ ing, reference numeral 1 and 2 indicate two support platforms, generally alike one to the other, that are carried by respective support structures. The support structures are not illustrated in the drawing as they are well known, made like the ones cited in the prior art statement. The platforms 1, 2 are indirectly moved by related pairs 10, 20 of hydraulic cylinders 3, 4, namely a first pair and a second pair. The stems 3a, 4a of the cylinders 3, 4 be¬ longing to the same pair of cylinders, are made to move in synchrony with each other, as mentioned in the prior art statement. The cylinders 3 of the first pair 10 are connected to related conduits 5 that include respec¬ tive cutoff solenoid valves 6 and that converge to a branch point 7 of a first pipe 8. In a similar way, from the cylinders 4 of the second pair 20 related conduits 9 depart, which include cutoff solenoid valves 11 and which converge to a branch point 12 of a second pipe 13. The pipes 8 and 13 are connected to a flow splitting valve 14 that is in turn connected to a main duct 15 departing from an electrohydraulic unit 50, of known type. The first pipe 8 is also connected to the main duct 15 via a first channel 30. This connection is set or removed by means of a first synchronisation solenoid valve 31, and a necking 42. The synchronising solenoid valve 31, 41 are controlled by an electronic control unit 100, that is connected to sensor means first 17 and second 18 respectively adapted to detect, second by second, the length of each of the part of the stems 3a and 4a that is outside the respective cylinder. For this purpose these sensor means are positioned near the stems. The electronic unit 100 processes the signals delivered by the sensor means 17, 18 in order to estimate how much the stems 3a, 4a have come out of the cylinders. While raising, the detection of a condition in which the difference between the coming out of the stems 4a and 5he stems 3a is over a prefixed value, causes intermittent operation of the first synchronising solenoid valve 31, in case this dif¬ ference is greater that zero. If this difference is negative, then the second synchronising solenoid valve is operated. Operation of one of these valves provokes a pulse with higher pressure in the first pipe 8 or in the second pipe 13 respectively, which pulse allows a greater volume of fluid to flow in the first hydraulic cylinders pair 10 or in the second hydraulic cylinders pair 20, respectively. This additional amount of fluid reduces the difference in the coming out of the stems 4a and 3a. This operating style is performed until the difference in the coming out of the stems 4a, 3a take a value less than the tolerance that has been prefixed. In the same way, while lowering, the detec¬ tion of a condition like the one just mentioned, causes operation, for a short time, of the second synchronising solenoid valve 41, in case the differ¬ ence is greater than zero. If the difference is negative, the first synchronising solenoid valve 31 will be operated. Operation of one of these synchronising solenoid valves, provokes a pulse with lower pres¬ sure in the second pipe 13 or in the first pipe 8, respectively, which pulse allows a greater volume of fluid to go out of the second hydraulic cylinders pair or out of the first hydraulic cylinders pair respectively, thus reducing the difference in the coming out of the stems 4a and 3a. This operating cycle goes on until the dif¬ ference between the coming out of the stems takes a value less than the prefixed tolerance. On one hand, the advantages coming from the present invention are basically technical ones, in that any nonalignment, in the horizontal plane, occurring for the support platforms of a hydraulic lifting device is promptly definitely eliminated. On the other hand, the advantages are econo¬ mical since the lifting device that incorporates the invention can be manufactured with flow splitting valves which are very simple in construction and thereof very cheap. Obviously, the invention has been described with reference to the accompanying drawings as an example only and has not any limitative aim. Therefore, it is understood that all the variation suggested by practical use, manufacturing and exploitation, can be incorporated in the inven¬ tion as defined by the following claims. For example, each of the support platforms can be moved either by only one hydraulic cylinder or by more that two hydraulic cylinders.

Claims: CLAIMS 1. Electrohydraulic lifting device, including: at least two support platforms (1, 2) set substanti- ally parallel to each other and carried by related structures made in such a way as to define two extreme positions for the platforms, namely a low¬ ered position and a raised position respectively; at least two hydraulic cylinders, namely a first cylinder (3) and a second cylinder (4) each arranged for operating a respective one of the said struc¬ tures; a flow splitting valve (14) connected at one side to pipes, namely a first pipe (8) and a second pipe (13) each connected to a related one of the said hydraulic cylinders (3, 4) ,- an electro-hydraulic central unit (50) connected, through a main conduit (15) , to the other side of the said flow splitting valve (14) and provided for feeding the said hydraulic cylinders (3, 4) ; the said lifting device being characterised in that it also includes: a first duct (30) aimed at connecting said first pipe (8) with said main conduit (15) , via a first synchronising solenoid valve (31) ,- a second duct (40) aimed at connecting said second pipe (13) with said main conduit (15) , via a second synchronising solenoid valve (41) ,- a first sensor means (17) aimed at detecting the length of the part of the stem (3a) that is outside the related first hydraulic cylinder (3) ,- a second sensor means (18) aimed at detecting the length of the part of the stem (4a) that is outside the related second hydraulic cylinder (4) ; an electronic unit (100) , to which the said first and second synchronising solenoid valves (31, 41) as well as the said first and second sensor means (17, 18) are connected, the said electronic unit (100) being designed to process the electronic signals supplied to it by the said sensor means and to operate the one or the other of the said synchronis¬ ing solenoid valves (31, 41) , as a consequence of a negative or positive value of the difference between the parts of the said stems (3a, 4a) coming out from the respective cylinders, so that this difference is made to fall within a prefixed tolerance range. 2. Electrohydraulic lifting device, characterised in that operation of the said synchronising solenoid valves (31, 41) is performed in intermittent manner.

Inventors: MANGANELLI FAUSTO, MANGANELLI, FAUSTO
Applicants: MANGANELLI FAUSTO, RAVAGLIOLI SPA, MANGANELLI, FAUSTO, RAVAGLIOLI S.P.A.
Application year: 1994
Main classification: B66F7
IPC codes: B66F7, F15B11